The present invention relates generally to otologic prostheses; and more particularly to a novel and improved otologic prosthesis for relieving impaired conductive hearing of the middle ear.
Otosclerosis is a common cause of progressive conductive hearing loss in which softening and hardening of minute areas of the ossicles (malleus, incus and stapes) in the middle ear produce abnormal bone growth and impede conduction of sound vibration from the eardrum to the inner ear. In about ten percent of patients with otosclerosis, the bone growth spreads to the stapes bone in particular, the final link in the middle ear chain. The stapes is a small stirrups-shaped bone with its base resting in a small groove, commonly called the oval window, in intimate contact with the inner ear fluids. When the amount of otosclerosis at this location is significant, as determined by careful hearing tests, a stapedectomy (or stapedotomy) is the treatment of choice.
A stapedectomy is a microsurgical technique in which a portion of the stapes or stapes arch is replaced by a prosthesis. When the procedure was first introduced in the 1950s, many surgeons became skilled in the technique and while many more surgeons, on an average, now perform it there are relatively few performed per surgeon. Hence, proficiency is harder to maintain for the occasional stapes surgeon.
A stapedectomy is usually performed through an incision in the ear canal under local or general anesthesia. A flap consisting of canal skin and the tympanic membrane (eardrum) is elevated and the posterior superior bony external auditory canal is drilled away to expose the stapes, incus, and chorda tympani (facial nerve). The ossicles are palpated to confirm fixation of the stapes and mobility of the malleus and incus.
With care taken to preserve the chorda tympani, the joint between the incus and the stapes is separated with a knife, and a laser or other microsurgical instrument severs the stapes tendon and one crus (leg) of the stapes. The arch of the stapes bone may then be removed by fracturing off the other crus allowing the footplate to remain in the oval window. A laser is used to form a minuscule hole in the footplate for posting the stapedial prosthesis. In some cases, the footplate is also removed by a so-called xe2x80x9clarge holexe2x80x9d technique and a vein grafted to the internal wall of the tympanum to cover the opening and to support the prosthesis.
After a hole is made in the footplate (or tissue is placed over the opening to the inner ear made after removing the footplate) one end of a biocompatible plastic or metal piston-like stapedial prosthesis of proper length is posted in the hole and the other end attached to the incus. A piece of fat or other tissue is taken, such as from a small incision behind the ear lobe, to seal any hole in the window, and the eardrum is folded back into its normal position with a small gelatin sponge to hold it in position.
A critical part of the procedure is attaching the prosthesis around the lenticular process of the incus due to its minuteness and delicate nature, typically about 3.5 mm to 6 mm long and 0.6 mm to 0.8 mm diameter. For instance, in U.S. Pat. No. 5,370,689 to Causse one end of the prosthesis fabricated of PTFE is posted in a hole drilled in the exposed footplate and a split eyelet at the other end must be crimped around the incus. In U.S. Pat. No. 3,714,869 to Shay Jr. one end of the prosthesis is placed on a vein graft invaginated into the oval window, and a split eyelet at the other end must be forced open by elastic deformation to fit onto the incus. Elastic recovery capacity of the eyelet causes it to restore to its original form in about 20 minutes and grip the incus firmly. U.S. Pat. No. 3,838,468 to Armstrong discloses a stapedial prosthesis for use in cases where the footplate is also removed. A piston is fixed at one end to a vein graft for covering the oval window. A wire of stainless steel, platinum, gold, or like biocompatible material shaped like a shepherd""s crook extending from the other end, is crimped about the lenticular process of the incus. U.S. Pat. No. 5,433,749 to Clifford et al. discloses a stapedial prosthesis of metal or plastic in which one end of a piston extends into the fluid in the inner ear and the other end is secured to the incus by a separate heat-shrinkable sleeve when heat is applied as by a laser.
It is readily apparent that great care and skill are required to secure these and similar prostheses to the lenticular process of the incus. The minute size of the prostheses also makes them extremely difficult to manipulate into proper position for tightening around the incus, even with state-of-the-art microsurgical instrumentation. Once in place, if the prosthesis is not tightened sufficiently about the incus, fluctuating hearing loss, dizziness, or extrusion of the prosthesis may occur. If it is too tight, necrosis of the incus may occur. In. either case, the tightening procedure in itself may cause trauma to the delicate middle ear structures, including fracture or subluxation (dislocation) of the incus.
Other otologic prostheses may be implanted by similar procedures directly between the malleus and the footplate of the stapes or the oval window of the inner ear.
This invention features an otologic prosthesis which can be installed easily with confidence by the occasional ossicle replacement surgeon and with few complications and good hearing results.
The invention also features an otologic prosthesis, which can be readily connected to an ossicle with little trauma to the delicate middle ear structures.
The invention further features a stapedial prosthesis which is relatively simple in construction, utilizes state-of-the-art materials, and which can be easily manipulated in the middle ear.
In one general aspect of the invention, an otologic prosthesis of biocompatible shape memory alloy for conducting sound vibration from the eardrum, through the inner ear, to the oval window of the inner ear. One embodiment of the invention is a stapedial prosthesis including a shaft of nickel-titanium wire having means on one end portion for posting in a hole formed in the footplate of the stapes. The other end portion of the shaft, in a thermoelastic martensitic phase, is reversely turned to form a bight, as manufactured, to fit snugly around the lenticular process of the incus when installed. The bight is plastically deformable at ambient temperatures to fit loosely against the incus. When the wire temperature is elevated to a higher temperature, as by application of a laser beam, the bight returns to its memorized shape for positively embracing the incus. Preferably, a heat sink flange is mounted on the shaft for conducting heat to the bight when the laser energy is applied. Other embodiments of prostheses are disclosed.
In one aspect, the invention features an apparatus having an elongated member with a first end and a second end. The first end defines a first bight lying substantially in a first plane. The first end is deformable to open the first bight to receive a first otologic structure and configured to substantially close the first bight in response to an applied signal thereby to capture the first otologic structure. The second end defines a second bight lying substantially in a second plane transverse to the first plane. The second end is deformable to open said second bight to receive a second otologic structure and configured to substantially close the second bight in response to an applied signal thereby to capture the second otologic structure with the second bight.
In another aspect, the invention features an apparatus having an elongated member with a first end and a second end. The first end defines a first bight lying substantially in a plane. The first end is deformable in response to an applied signal to open the first bight to receive an otologic structure. The first end is configured to substantially close the first bight in response to an applied signal thereby to capture the first otologic structure. The second end defines a second bight lying substantially in the plane. The second end is deformable in response to an applied signal to open the second bight to receive a second otologic structure. The second end is configured to substantially close the second bight in response to an applied signal thereby to capture the second otologic structure.
In another aspect, the invention features an elongated member having a first end and a second end. The first end defines a first bight lying substantially in a first plane. The first end is deformable in response to an applied signal to open the first bight to receive a first otologic structure. The first end is configured to substantially close the first bight in response to an applied signal thereby to capture the first otologic structure. The second end of the member includes an enlarged surface area sized and oriented to lie substantially flat against and be secured to a second otologic structure. The second end receives sound vibrations from the second otologic structure.
In another aspect, the invention features a method including providing an otologic implant having an end defining a bight. The end is deformed to open the bight to receive an otologic structure. Applying a signal to the implant substantially closes the bight and captures the otologic structure.
Preferred embodiments may include one or more of the following features. The first otologic structure is a malleus or an incus and the second otologic structure is a portion of the stapes arch or a capitulum. The member is formed of biocompatible, shape-memory alloy.
The enlarged surface is substantially planar and is oriented at an angle to the member within a range of about 30 degrees to about 90 degrees. The first otologic structure is an incus, a portion of the stapes arch, or a capitulum and the second otologic structure is an eardrum. The apparatus includes an adhesive.
The provided implant includes a first end defining a first bight and a second end defining a second bight. The first end is deformed to open the first bight and the second end is deformed to open the second bight. A signal applied to the implant captures the first otologic structure and the second otologic structure. The signal is heat. The otologic structure is a malleus.
Embodiments of the invention may have one or more of the following advantages. The shape-memory alloy permits at least one end of the implant to be secured to an otologic structure without having to insert a securement tool in the middle ear. The implant may be deformed to a shape that readily permits positioning of the implant to capture an otologic structure. A surgeon controls the initiation of returning the prosthesis to its predetermined shape. The prosthesis combines heat-activated capture of an otologic structure with the structural properties of a metal alloy.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.